The invention relates to a ventilation panel comprising a rectangular plate-shaped grating for shielding electromagnetic radiation arranged in a rectangular frame and composed of cells.
A plate-shaped grating of the kind mentioned in the opening paragraph is known from U.S. Pat. No. 3,821,463. This grating may be made, for example, of aluminium strips absorbing elelctromagnetic radiation. According to p. 95 and 96 of a catalogue published by "Metex Electronic Shielding Group" (entitled: "EMI/RFI Shielding Handbook and Catalogue") in 1977, such a grating can be clamped in a frame having a U-shaped cross-section so that a unit serving as a ventilation panel is obtained. For this purpose, the frame is provided, for example, with projections which penetrate into the material of the grating. The panel thus formed can then be secured by means of screws extending through the frame and the grating on a wall of a device (box) which has to be electromagnetically shielded while maintaining the cooling by natural convection of the heat-producing electrical components present in the box. Between a wall of the said box and the ventilation panel there is clamped a further electromagnetic shield.
A disadvantage of the known ventilation panel is that tolerances of the U-shaped frame and the grating in a direction at right angles to the plane of the grating have to be neutralized by a considerable elastic deformation of the flanges of the comparatively rigid U-shaped frame, while plastic deformation of the cell structure has to ensure that a sufficiently large pressure force is obtained between the frame and the grating. The frame and the grating are consequently subjected to a comparatively high mechanical load. The invention has for its object to provide a ventilation panel in which the above noted disadvantage is avoided.